This invention relates to tufting machine gauge parts and more particularly to modular tuft-forming hooks for staggered needle cut pile tufting machines.
In the production of tufted cut-pile fabric each reciprocating needle cooperates with a looper or hook, the hook seizing a loop from the needle and holding the loop until it is cut by a knife acting in scissors-like fashion with the hook.
It has been found that the transverse pressure applied to the individual hooks by the respective knives can give rise to deflection of the tips of the hooks. The magnitude of the deflection, and, in consequence, the extent to which such deflection adversely affects accurate and consistent pick-up of yarn from the corresponding needle is determined, at least in part, by the closeness of the fit of the hook in the slot in the hook bar and by the length of the bill. Having regard to the manufacturing tolerances and clearances which must necessarily be provided, both in connection with the hook bar arrangement and the needle bar arrangement, it sometimes happens that the deflection of the hook tip in any instance is such as deleteriously to affect loop pick-up, with consequential impairment of the uniformity of the tufted fabric. Furthermore, in the event of damage to a series of hooks or when such hooks are worn, the replacement of a new set is particularly demanding of time.
To overcome these problems it has been proposed to provide in cut-pile tufting machines having in-line cooperating needles and identical in-line hooks, a hook mounting wherein the respective hook shanks are imbedded in a common body member in side-by-side disposition. Such constructions are illustrated in U. K. Design Nos. 980,060 and 980,062. This construction has the advantage of eliminating difficulties of aligning the hooks in the hook bar of a tufting machine since the hooks are aligned in the formation of the modules and each body member may have an alignment surface for clamping to a hook bar in the machine without the need for alignment of the individual hooks in the relatively uncontrolled conditions of a tufting mill.
It is also known in the art to provide tuft-forming instrumentalities for a tufting machine intended to produce cutpile fabric wherein the needles are arranged in staggered relationship on a needle bar and wherein those hooks intended for co-operation with respective ones of the row of needles furthest from the hook bar on which the hooks are mounted have a longer bill than the hooks intended for co-operation with the other row of hooks. For ease of aligning the hooks in the hook bar, the throats of both the long billed hooks and the remaining hooks may be in alignment in the longitudinal direction of the hook bar and each hook secured in position within a respective slot in the hook bar by screw means. A cutting knife is provided for each hook, and the individual knives are similarly aligned transversely of the machine. Tufting machines having this construction are illustrated in U.S. Pat. Nos. 4,003,321 and 3,913,505.
Although orginally proposed to minimize the deflection of the tips of the hooks in tufting machines having a staggered needle construction, the utilization of the modular concept also alleviates the need to provide aligned throats of adjacent hooks. The hooks may be positioned side-by-side in a module body member with the throat portion of adjacent hooks laterally spaced in the module by the amount of the staggered offset pitch of the tips of the bills or some other convenient amount. Difficulties, however, may develop after the hooks have been operating for some time. Since the knives act against the edge of the cooperating hooks, wear on the hooks occurs. The individual hooks of a module cannot be replaced without destroying the module body member so regrinding of the knife engaging position of the hooks has been proposed. Conventionally hooks have been reground by grinding the face of the hook against which the knife acts to again obtain a sharp cutting edge. However, grinding of the hooks of an integral modular assembly of hooks, especially when the hook gauge, i.e., space between adjacent hooks is in the order of less than 0.1 inch, creates difficulties since there is no adequate space between the hooks for receiving the grinding wheel.